Modern vehicles, such as automobiles, are typically offered to consumers in a wide variety of paint colors. In fact, from model year to model year, it is not uncommon for a particular vehicle model to be available in several new paint colors. Variations in the actual paint color and appearance of the paint color may arise from a number of factors, such as changes in paint formulation, effect degradation, and variations in the paint application process or equipment. Consequently, when a vehicle's body panels are damaged and require repairs (including repainting), the paint manufacturer supplies one or more paint formulations for the original paint color to customers, such as repair shops.
By supplying a plurality of formulations or variants for a particular color, the paint manufacturer accounts for those factors which affect the actual color. Typically, the formulations for a particular color are distributed to repair shops on paper, microfiche, or compact disks (CD). A color tool, composed of swatches of the variants for each color, may also be produced and delivered to each customer.
The customer must then attempt to select which formulation most closely matches that part to be painted. This is typically done visually by comparing swatches to the part or by spraying a test piece with each formulation.
Different formulations can be derived from actual data gathered by inspectors at various locations such as the automobile manufacturer or vehicle distribution point. The inspectors also take color measurement readings from new automobiles which have a particular paint color. These readings are used to develop a variety of color solutions, i.e., different paint formulations for the same color.
There are several disadvantages to the present method of color matching the part to be painted in this manner. Conventional color laboratories mainly use human analysis to determine color match quality. This method requires significant numbers of people, equipment and materials for identifying pigments and locating a close match from a database. In some cases, an existing formula may provide a close match. In other cases, the formula must be adjusted, mixed, sprayed and compared to the standard. This step is repeated until a suitably close match is found. In still other cases, no match is found and a formula must be developed from scratch. Correction of the formula requires a highly skilled technician proficient in the interaction of light with several different pigments.
Moreover, traditional computer software that assists a technician has several disadvantages. Traditional computer software has not proven to be very effective on colors containing “effect pigments.” This software is typically based on a physical model of the interaction between illuminating light and the coating. These models involve complex physics and do not account for all aspects of the phenomena. A traditional approach is to use a model based on the work of Kubelka-Munk or modifications thereof. The model is difficult to employ with data obtained from multi-angle color measuring devices. One particular difficulty is handling specular reflection that occurs near the gloss angle. Another deficiency of the Kubelka-Munk based models is that only binary or ternary pigment mixtures are used to obtain the constants of the model. Thus, the model may not properly account for the complexities of the multiple interactions prevalent in most paint recipes.
Acceptable tolerances of a color match vary depending on the color. Tolerances are typically expressed in differential color values, e.g., ΔL*, ΔC*, ΔH* or ΔL*, Δa*, Δb*. The differential values will vary as a function of the color. Historically, these values have been determined manually, i.e., by visual evaluation. The tolerances for a formulation are determined as a function of all of the color measurement values which have been deemed acceptable (usually by visible methods). Attempts have been made to build uniform tolerance equations from the differential color values. These equations are not wholly adequate and still require the establishment of various parameters by the user for a particular application.
The present invention is aimed at one or more of the problems identified above and provides a unique method of determining an acceptability of a color match.